The object of this project is the development of a parathyroid hormone (PTH) bioassay based on the high sensitivity of suspensions of target-tissue-cells to hormone stimulation. Evaluation of hormone activity is done through measurement of 3'5'-cyclic-AMP accumulation in cell suspensions or microsomal membranes prepared from target tissues. The cells are separated by mild enzymatic digestion from bone, cartilage or tumors (osteosarcoma). The microsomes are prepared by differential centrifugation. Attempts will be made to establish PTH-sensitive cell lines through the culture of cells selected by affinity chromatography and cloning for PTH receptors.